Q: My wife and I have a 3-year-old son. We are very much on the same page when it comes to the “tough love” issues of discipline, limiting TV and junk food, etc. It’s worked out well so far — we have a very happy and well-behaved child, who seems to be on the right developmental track.

Every year we spend a week with my family at a beach house. My sister and her husband have slightly older kids. As parents they are heavy on indulgence and light on discipline (putting it mildly).

We anticipate that one year, our kid will ask why his cousins get to do and eat whatever they want, while he doesn’t (he would watch “SpongeBob” and eat cookies all day if he could). I wouldn’t know quite what to say in the presence of my sister’s family that would (a) be honest (b) not offend them and (c) satisfy our kid’s sense of fairness in the world. Any advice?

A: Your sister might well be too lenient with her spawn, but unless you intend to make a direct statement to your sister about her choices, it’s best to make no statement at all.

It’s also best not to draw a straight line between your parental choices and your child’s excellence; hubris has no place in the insanely complex series of causes and effects that creates a well-adjusted child.

So when the cousins are eating Crap Flakes straight from the box while your kid asks why he has to eat homemade granola, have a bland, stock answer ready, along the lines of “Different families, different ways.”

“Different ways” are something your son will have to get used to anyway — the annual beach week hardly will be the only time this comes up. Save the longer explanations for calm moments at strategic intervals, to teach him about nutrition, hard work, the reasoning behind your ways.

You might also want to talk to your wife about bending judiciously on “special” occasions someday. As your boy gets older, the need for absolute consistency wanes while the benefits of a surprising “yes” start to accrue. Living in the mainstream means your son will grow up amid junk temptations in every aspect of life. You have to control his access to junk, of course — but take that control too far and you’ll have a rebellion on your hands, by a kid who hasn’t been allowed to learn for himself how and where to draw lines.